Method and apparatus for producing displays utilizing an electronic display system

ABSTRACT

Disclosed herein is a thermal display system including a plurality of very small isolated semiconductor mesas or bodies, each of which contains a heater element so that when the heater element is energized a &#39;&#39;&#39;&#39;hotspot&#39;&#39;&#39;&#39; is formed at the top surface of the mesa to provide a localized dot of heat. By interposing an energy or heat transferable coating, such as carbon paper, for example, between the mesas and a display medium, which preferably is nonsensitized, and selectively energizing certain mesas to form selective hotspots, the heat produced thereby thermally transfers said transferable coating with the display medium, thereby to produce an information representation on the display medium.

United States Patent [72] lnventor William A. Ekton Houston, Tex.

[21] A'ppl. No 823,128

1221 Filed May a, 1969 [45] Patented July 27, 1971 [73] Assignee TexasInstruments Incorporated Dallas, Tex.

[54] METHOD AND APPARATUS FOR PRODUCING DISPLAYS UTILIZING AN ELECTRONICDISPLAY 385, 543; 101/93 RC;.17S/'3.0;"179/100.2 A;197/1s1,172;34o/174.1 r; 346/49, 74. 76, 107,

108 56] References Cited UNITED STATES PATENTS 2,713,822 7/1955 Newman2,917,996 12/1959 Epstein et al. .1 346/76 UX 3,273,686 9/]966 Ploeger,.lr [97/172 3,453,648 7/1969 Stegenga 346/76 3.496.333 2/1970 Alexanderet al 219/216 ABSTRACT: Disclosed herein is a thermal display systemincluding a plurality of very small isolated semiconductor mesas orbodies, each of which contains a heater element so that when the heaterelement is energized a hotspot is formed at the top surface of the mesato provide a localized dot of heat. By interposing an energy or heattransferable coating, such as carbon paper, for example, between themesas anda display medium, which preferably is nonsensitized, andselectively energizing certain mesas to form selective hotspots, theheat produced thereby thermally transfers said transferable coating withthe display medium, thereby to produce an information representation onthe display medium.

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PATENTED JUL27 I971 SHEET 3 OF 3 METI'IOD AND APPARATUS FOR PRODUCINGDISPLAYS UTILIZING AN ELECTRONIC DISPLAY SYSTEM This invention relatesgenerally to electronic display systems and more particularly toelectronically controlled thermal display systems.

It is known in the art to fabricate an electronic display systemcomprised of a plurality of very small air isolated semiconductor mesasor bodies mounted on a ceramic chip by a thermally insulating layer ofepoxy. According to one form, each of the mesas includes a diffusedresistor in the collector circuit of a diffused transistor. Currentthrough the collector resistor is controlled by a pulse applied to thebase of the transistor, thus raising the mesa to an elevated temperaturethereby causing a hotspot" to appear on the face of the mesas. The mesasmay be selectively energized by a character generating logic circuit ina manner to specially reproduce the character which may be viewed bychanging the color of a thermochromic material or by changing the colorof a thermally sensitive paper disposed adjacent to the mesas orprintheads. However, the color change (information representation)produced on the thermally sensitive display medium by the hotspot is notarchival (permanent). Exposure to sunlight or normal aging, for example,causes the representation to fade. Furthermore, with the thermalsensitive paper, printhead temperatures between 175 C and 225 C areneeded to cause an information representation to form on the displaymedium.

The thermally sensitive paper, which is in direct contact with the mesasof the printhead, not only subjects the printhead to wear, residuebuildup from the thermal coating on the paper, and sticking, but also ismore expensive than basic paper (nonsensitized paper).

Accordingly, it is an object of this invention to provide an improvedsimpler thermal display system and method for producing thereon aninformation representation on a nonsensitized medium.

Another object of the invention is to provide a thermal display systemwhich will produce an archival reproduction on a display medium.

Another object of the invention is to provide a thermal display systemwhich will produce an archival reproduction on a nonsensitized displaymedium.

Still another object of the invention is to produce a thermal displaysystem which requires lower printhead temperatures than are required toactivate most thermochromic paper for producing an informationrepresentation on a display medium.

Still another object of the invention is to provide a display systemusing a low cost display medium, such as a nonsensitized paper.

Other objects, features and advantages of the invention may be bestunderstood by a reference to the following detailed description whenread in conjunction with the accompanying drawings, in which likereference numerals indicate like parts and in which:

FIG. I is an enlarged view ofan electronic printhead;

FIG. 2 is a schematic circuit diagram of a heater element of the thermalprinthead of FIG. 1;

FIG. 3 is an isometric view partially broken away of an electronicprinthead and carriage assembly therefor usable in a thermal printeraccording to the present invention;

FIG. 4 is an enlarged front view of the electronic printhead assemblyshown in FIG. 3;

FIG. 5 is an isometric view of an electronic thermal printer utilizingthe electronic printhead and carriage assembly shown in FIG. 3;

FIG. 6 is a top view of the printhead, heat transferable material anddisplay medium; and

FIGS. 7 and 8 illustrate another embodiment of the present invention.

Referring now to FIGS. l4, a thermal printhead of the type, for example,described and claimed in various aspects in copending US. Pat.application, Ser. No. 67l,82l, filed Sept. 29, 1967, entitled IntegratedHeater Element Array and Drive Matrix and Method of Making Same,"assigned to the assignee of the present application, is indicatedgenerally by the reference numeral 10. The printhead 10 is composed of a5 X 5 matrix of semiconductor mesas or bodies 12, which are thermallyisolated from one another by airgaps, as best seen in FIG. 1, and whichare bonded to a ceramic chip or substrate 0 14 by a thermally insulatingepoxy layer 16. A transistor 18 and a resistor 20 (see FIG. 2) arediffused into the interior of each mesa or body 12 adjacent the epoxylayer 16. A buffer transistor 22 (see FIG. 2) for each of the 25 mesasI2 is diffused into the face of semiconductor chip 24, generally withinthe area designated by the dotted outline 26 (see FIG. 4), the printheadcircuits and the buffer circuits being interconnected by thin metallicfilm leads (not illustrated) on the surface of the semiconductor mesas12 and the chip 24 adjacent the epoxy layer 16. The ceramic chip 14 isthe bonded to a metallic heat sink 28. The leads from the bases of thebuffer transistors 22 terminate around the periphery of thesemiconductor chip 24, and are bonded to leads 30 on a printed circuittemplet 32 mounted on the heat sink. The leads 30 on the printed circuittemplet are soldered to the leads of a multilead strap 34 which, inturn, are interconnected to character generating logic circuits (notshown). The printhead assembly as illustrated in FIG. 3 may be utilizedin a thermal printer such as the one illustrated in FIG. 5.

FIG. 5 illustrates an electronic thermal printer utilizing the presentinvention and indicated by the reference numeral 40. Two end plates 42and 44 provide the support for feeding the display medium 46, which can,for example, be either thermally sensitive paper or nonsensitive paper,from a large roll fed from spool 48. The electronic printhead andcarriage therefor, indicated generally by the reference numeral 28 (andshown in detail in FIG. 3) is secured to driving mechanism 49 which isslidably mounted on cylindrical rods 50 and a conventional steppingmotor in mechanism 49 (not shown in detail) steps the carriage from leftto right after the character print portion of the printing cycle, andupon completing the printout ofa line drives the printhead carriage backto the left-hand margin position. Supports 51 and 52 are connected toend plates 42 and 44, respectively. An energy or thermally transferablecoating 54 (for example, a carbon composition such as a wax mixed withcarbon particles or other suitable pigment) and support therefor 56 (seeFIG. 6) is between the carriage 28 and the display medium 46. Thiscoating 54 may be on a thin, flexible material 56, such as paper, or aplastic such as polyester (Mylar), polyethylene, polyimide (H-film), orthe like, and is moved, for example, as a ribbon 56 past the carriage 28by takeup reel 58 and feed reel 60 located on supports 51 and 52,respectively. The thermally transferable coating 54 and support material56 may be a conventional carbon ribbon of the type, for example, usedwith conventional impact mechanical typewriters, by way of a furtherexample.

FIG. 6 illustrates the respective positions of the printhead 10 andmesas 12 with regard to the display medium 46, thermally transferablecoating 54, and thin, flexible support material 56.

In the operation of the electronic printer illustrated in FIG. 5, theelectronic carriage assembly 28 is successively stepped across thedisplay medium 46 from left to right by a motor in mechanism 49. At eachsuccessive position, selective mesas 12 are energized, thereby producinghotspots at the surface of the mesas. The heat generated by the selectedmesas passes through material 56 which, in turn, causes the thermallytransferable coating 54 to transfer onto the display medium 46 which, aspreviously stated, may be sensitized or nonsensitized paper (see FIG. 6)passing in contact therewith. Accordingly, the heat from the selectedmesas I2 is thermally coupled through material 56 to coating 54. With acarbon and wax composition, for example, selective heating of mesas l2softens the wax making it sticky at the outer surface 54 enabling it totransfer to the display medium 46 and adhere to the display medium toform information representation 110. The back surface of coating 54(adjoining the support medium 56) due to its proximity to mesas 12 is ata higher temperature which makes coating 54 very weak at this interfaceand readily separable from it. Accordingly, this technique allows theuse of basic, conventional (nonsensitized) paper instead of the morecostly use of thermal sensitive paper as a display medium which effectsa potential cost savings. This printing cycle is repeated until theprintout for the particular line is completed, at which time thecarriage assembly 28 is returned to the lefthand margin position,display medium 46 is advanced one line by advance means (not shown) andfed from spool 48, and the takeup reel 58 is appropriately advanced bymeans (not shown) to allow additional unused portion of the coating 54to come into contact with the printhead 10.

With the embodiment shown in FIG. 5, the temperature required of thermalprinthead 10 to obtain an information representation on display medium46 ranges between 100 C to 125 C. If a higher printhead temperature isrequired (in order to obtain faster speed of operation of printer 40),such as between 175 C and 225 C, it is either desirable to insure thatthe service temperature of the material 56 (shown in FIGS. 5 and 6)exceeds the operating temperature of the printhead, or if the supportmaterial 56 has a service temperature less than the operatingtemperature of the printhead 10, to interpose a high temperatureinsulator between the thermal printhead l0 and the support material 56to insure that the softened support material 56 does not adhere toprinthead 10, such as is shown in FIG. 7.

FIG. 7 illustrates an electronic thermal printer indicated generally bythe reference numeral 70. The display medium 46, which may be plainpaper, is fed from spool 74 and supported by roller 75. The thermallytransferable coating 54 is on support material 56 (see FIG. 8) and isdistributed by spool 72 over reel 78. Similar to the embodiment shown inFIG. 5, the heat transferable coating may be a carbonlike compositionand the support material may be paper or plastic, such as polyethylene(which has a service temperature of approximately 125 C). Interposedbetween the thermal elements 12 and the support material 56 is atemperature insulator material 80'capable of withstanding the printtemperature of the thermal printhead elements on printhead 10. Thistemperature insulating material is shown in FIG. 7 as a ribboninterconnected between feed reel 82 and takeup reel 84. This hightemperature insulator material could be a high temperature plastic, suchas polyimide, which has a service temperature of 400 C, which is well inexcess of the 175 C to 225 C printhead temperature rangebeforementioned.

Operation of printer 70 is similar to that described with regard to FIG.5, with the addition that printhead 10 may operate in the range of 175 Cto 225 C and the heat generated by the thermal mesas or bodies 12 onprinthead 10 is thermally transferred through both the temperatureinsulator material 80 and the support material 56 to form an informationrepresentation on display medium 46.

Although the support material 56 and energy transferable coating 54 areshown in a ribbon format and in sheets supplied from different spools,other configurations are possible, such as the support material 56 andtransferable coating 54 and the display medium 46 could be supplied fromthe same spool or physically attached. The 5 X 5 array of mesas is givenherein as an example only since any number and shape of the array may bechosen, depending upon the character of the information desired to bedisplayed on the display medium.

It is to be understood that the above-described embodiment and method ismerely illustrative of the invention. Numerous other arrangements may bederived by those skilled in the art 5 thermal printhead having thermalelements therein, a display medium, a support material between saidelements and said display medium, a thermally transferable coating onsaid material adjacent to said display medium, and a high temperatureinsulator material interposed between said thermal ele- 0 ments and saidsupport material.

2. A thermal display system according to claim 1 wherein said displaymedium is nonsensitive paper.

3. A thermal display system according to claim 1 wherein said insulatoris plastic.

4. A thermal display system according to claim 3 wherein said plastic ispolyimide.

5. A thermal display system comprising in combination a substrate, anarray of semiconductor bodies upon one surface of said substrate, saidarray being so arranged that select ones of said bodies define a form ofinformation representation, heater elements within each of said bodies,means for selectively energizing said heater elements thereby to heatsaid select ones ofsaid bodies, a display medium, a thermallytransferable coating between said semiconductor bodies and said displaymedium and an insulating material interposed between said thermallytransferable coating and said semiconductor bodies.

6. A thermal display system comprising in combination a substrate, anarray of semiconductor bodies upon one surface of said substrate, saidarray being so arranged that select ones of said bodies define a form ofinformation representation heater elements within each of said bodies,means for selectively energizing said heater elements thereby to heatsaid select ones of said bodies, a nonsensitized display medium, a thin,flexible material having a thermally transferable coating on one facethereof, said one face being positioned in thermal contact with saiddisplay medium, and an insulating material disposed intermediate saidflexible material and said semiconductor bodies whereby saidtransferable coating is transferred 40 from said flexible material tosaid nonsensitized display medium to form said informationrepresentation thereon in response to energization of said selectedheater elements.

7. A thermal display system according to claim 6 wherein said thin,flexible material and said thermally transferable coating constitute acarbon ribbon.

8. A thermal display system according to claim 6 wherein said thin,flexible material and said thermally transferable coating constitute acarbon paper.

9. In a thermal display system wherein preselected elements of a thermalprinthead are heated to effect a display of information on anonsensitized paper, a method for producing an archival copy of saidinformation wherein the improvement comprises the steps of:

a. selecting respective elements required to form a pattern of thedesired information representation;

b. positioning a thermally transferable coating between said thermalprinthead and said paper;

c. positioning a thermally insulating material intermediate said thermalprinthead and said thermally transferable coating; and

d. heating said selected elements to effect a transfer of said coatingonto said paper in regions corresponding to said preselected elements.

10. The method as set forth in claim 9 wherein said printhead is heatedto a temperature in the range of 175 C to 225C.

11. The method as set forth in claim 9 wherein said thermallytransferable coating comprises a carbon ribbon.

1. A thermal display system comprising in combination a thermalprinthead having thermal elements therein, a display medium, a supportmaterial between said elements and said display medium, a thermallytransferable coating on said material adjacent to said display medium,and a high temperature insulator material interposed between saidthermal elements and said support material.
 2. A thermal display systemaccording to claim 1 wherein said display medium is nonsensitive paper.3. A thermal display system according to claim 1 wherein said insulatoris plastic.
 4. A thermal display system according to claim 3 whereinsaid plastic is polyimide.
 5. A thermal display system comprising incombination a substrate, an array of semiconductor bodies upon onesurface of said substrate, said array being so arranged that select onesof said bodies define a form of information representation, heaterelements within each of said bodies, means for selectively energizingsaid heater elements thereby to heat said select ones of said bodies, adisplay medium, a thermally transferable coating between saidsemiconductor bodies and said display medium and an insulating materialinterposed between said thermally transferable coating and saidsemiconductor bodies.
 6. A thermal display system comprising incombination a substrate, an array of semiconductor bodies upon onesurface of said substrate, said array being so arranged that select onesof said bodies define a form of information representation heaterelements within each of said bodies, means for selectively energizingsaid heater elements thereby to heat said select ones of said bodies, anonsensitized display medium, a thin, flexible material having athermally transferable coating on one face thereof, said one face beingpositioned in thermal contact with said display medium, and aninsulating material disposed intermediate said flexible material andsaid semiconductor bodies whereby said transferable coating istransferred from said flexible material to said nonsensitized displaymedium to form said information representation thereon in response toenergization of said selecTed heater elements.
 7. A thermal displaysystem according to claim 6 wherein said thin, flexible material andsaid thermally transferable coating constitute a carbon ribbon.
 8. Athermal display system according to claim 6 wherein said thin, flexiblematerial and said thermally transferable coating constitute a carbonpaper.
 9. In a thermal display system wherein preselected elements of athermal printhead are heated to effect a display of information on anonsensitized paper, a method for producing an archival copy of saidinformation wherein the improvement comprises the steps of: a. selectingrespective elements required to form a pattern of the desiredinformation representation; b. positioning a thermally transferablecoating between said thermal printhead and said paper; c. positioning athermally insulating material intermediate said thermal printhead andsaid thermally transferable coating; and d. heating said selectedelements to effect a transfer of said coating onto said paper in regionscorresponding to said preselected elements.
 10. The method as set forthin claim 9 wherein said printhead is heated to a temperature in therange of 175* C to 225* C.
 11. The method as set forth in claim 9wherein said thermally transferable coating comprises a carbon ribbon.